Related name for reverse access in Django - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the related_name attribute in Django models?

The related_name attribute defines the name to use for the reverse relation from the related object back to this one. It lets you access related objects easily from the other side of the relationship.

beginner

How do you access all Book objects related to an Author if related_name='books' is set on the ForeignKey?

You can access all books of an author by using author.books.all(). The related_name 'books' creates this attribute on the Author instance.

beginner

What happens if you do NOT set related_name on a ForeignKey in Django?

Django creates a default reverse name by using the lowercase model name with '_set' appended. For example, if the model is Book, the reverse name will be book_set.

intermediate

Can two ForeignKey fields in different models use the same related_name?

No, related_name must be unique per model to avoid clashes in reverse relations. If two fields use the same name, Django will raise an error.

intermediate

How does related_name='+' affect reverse access in Django?

Setting related_name='+' disables the reverse relation. This means you cannot access the related objects from the other side.

What does related_name control in Django models?

A The primary key field name

B The database table name

C The name of the reverse relation from the related model

D The model's verbose name

related_name sets the attribute name for reverse access from the related model back to this model.

If you have author = ForeignKey(Author, related_name='books'), how do you get all books of an author?

A author.books.all()

B author.book_set.all()

C author.get_books()

D author.books_set.all()

The related_name='books' creates the attribute books on the Author instance.

What is the default reverse name if related_name is not set?

A related_set

B modelname_set

C reverse_name

D default_related

Django uses the lowercase model name plus '_set' as the default reverse name.

What does setting related_name='+' do?

A Disables reverse relation

B Sets reverse relation to default

C Creates a reverse relation with name '+'

D Raises an error

Using '+' disables the reverse relation, so no attribute is created on the related model.

Can two ForeignKey fields in different models share the same related_name?

A Yes, always

B Only if fields have different names

C Only if models are unrelated

D No, it causes a conflict

related_name must be unique per model to avoid reverse relation conflicts.

Explain what related_name does in Django and why it is useful.

Think about how you get from one model to related objects in the other direction.

Describe what happens if you set related_name='+' on a ForeignKey field.

Consider when you might not want the reverse link.

Practice

1. What does the related_name attribute do in a Django model's ForeignKey field?

easy

A. It sets the name used to access related objects from the other model.

B. It changes the database table name for the model.

C. It defines the primary key of the model.

D. It specifies the default ordering of query results.

Solution

1. Step 1: Understand the purpose of related_name

   The related_name attribute defines how you access related objects from the reverse side of a ForeignKey relationship.

2. Step 2: Identify what related_name affects

   It does not affect table names, primary keys, or ordering but sets the attribute name for reverse access.

3. Final Answer:

   It sets the name used to access related objects from the other model. -> Option A

4. Quick Check:

   related_name = reverse access name [OK]

Hint: related_name names reverse access from related model [OK]

Common Mistakes:

• Confusing related_name with table name
• Thinking it sets primary key
• Assuming it controls query ordering

2. Which of the following is the correct way to set a related_name in a Django ForeignKey field?

easy

A. author = models.ForeignKey(Author, reverse_name='books', on_delete=models.CASCADE)

B. author = models.ForeignKey(Author, related='books', on_delete=models.CASCADE)

C. author = models.ForeignKey(Author, related_name='books', on_delete=models.CASCADE)

D. author = models.ForeignKey(Author, relation_name='books', on_delete=models.CASCADE)

Solution

1. Step 1: Recall correct attribute name

   The correct attribute to set reverse access name is related_name.

2. Step 2: Check syntax correctness

   author = models.ForeignKey(Author, related_name='books', on_delete=models.CASCADE) uses related_name='books' correctly; others use incorrect attribute names.

3. Final Answer:

   author = models.ForeignKey(Author, related_name='books', on_delete=models.CASCADE) -> Option C

4. Quick Check:

   Use related_name= for reverse access [OK]

Hint: Use exact attribute name 'related_name' in ForeignKey [OK]

Common Mistakes:

• Using 'related' instead of 'related_name'
• Using 'reverse_name' or 'relation_name' which don't exist
• Missing on_delete argument

3. Given these models:

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    author = models.ForeignKey(Author, related_name='books', on_delete=models.CASCADE)
    title = models.CharField(max_length=100)

What will author.books.all() return?

medium

A. All Author objects related to that Book instance.

B. All Book objects related to that Author instance.

C. A syntax error because 'books' is not defined.

D. An empty queryset always.

Solution

1. Step 1: Understand related_name usage

   The related_name='books' allows accessing all Book objects from an Author instance using author.books.

2. Step 2: Interpret the method call

   author.books.all() returns a queryset of all Book objects linked to that Author.

3. Final Answer:

   All Book objects related to that Author instance. -> Option B

4. Quick Check:

   author.books.all() = related books [OK]

Hint: related_name lets you get all related objects easily [OK]

Common Mistakes:

• Thinking it returns Author objects
• Assuming syntax error due to related_name
• Expecting empty queryset without data

4. Identify the error in this model definition:

class Comment(models.Model):
    post = models.ForeignKey(Post, related_name='post', on_delete=models.CASCADE)
    text = models.TextField()

What problem will this cause?

medium

A. It will cause a syntax error because related_name cannot be 'post'.

B. It will cause a runtime error because TextField is not allowed here.

C. It will work fine without any issues.

D. It will cause a reverse accessor clash if Post already has a field named 'post'.

Solution

1. Step 1: Understand related_name uniqueness

   The related_name must be unique per model to avoid clashes.

2. Step 2: Analyze the name 'post'

   If Post model already has a field or reverse accessor named 'post', this causes a clash error.

3. Final Answer:

   It will cause a reverse accessor clash if Post already has a field named 'post'. -> Option D

4. Quick Check:

   related_name must be unique to avoid clashes [OK]

Hint: Avoid related_name same as model or field names [OK]

Common Mistakes:

• Assuming related_name can be any string without conflict
• Thinking related_name causes syntax error
• Believing TextField is invalid here

5. You have these models:

class Category(models.Model):
    name = models.CharField(max_length=50)

class Product(models.Model):
    category = models.ForeignKey(Category, on_delete=models.CASCADE)

You want to access all products of a category using category.items.all(). How should you modify the ForeignKey?

hard

A. Add related_name='items' to the ForeignKey in Product.

B. Change ForeignKey to ManyToManyField with related_name='items'.

C. Rename the ForeignKey field to 'items'.

D. Add related_query_name='items' to the ForeignKey.

Solution

1. Step 1: Understand reverse access naming

   To use category.items.all(), the ForeignKey must have related_name='items'.

2. Step 2: Check other options

   Changing to ManyToManyField or renaming the field won't create the desired reverse attribute. related_query_name affects query filters, not attribute names.

3. Final Answer:

   Add related_name='items' to the ForeignKey in Product. -> Option A

4. Quick Check:

   related_name sets reverse attribute name [OK]

Hint: Set related_name='items' to get category.items [OK]

Common Mistakes:

• Confusing related_name with related_query_name
• Changing field name instead of related_name
• Switching to ManyToManyField unnecessarily